what is variable "external" meant for in javascript

Question

I just found out that there is a variable called external exists in most browsers except IE. I have 2 question wrt to this

what is external - http://jsfiddle.net/EVBjU/
IE gives object doesn't support this property or method when i do console.log(external). how to fix this, considering it's just a variable

Thanks

What do you mean by "fix this"? Simply removing the logging statement will remove the error. — David Pärsson
– David Pärsson, Commented Jul 22, 2013 at 10:31
@DavidPärsson i know that but how do i fix a "object doesn't support this property or method" in general — aWebDeveloper
– aWebDeveloper, Commented Jul 22, 2013 at 10:32
There is no fix, since what you're doing is not supported. The only fix is to not do it. — David Pärsson
– David Pärsson, Commented Jul 22, 2013 at 10:35

nnnnnn · Accepted Answer · 2013-07-22 10:35:46Z

2

"but how do i fix a "object doesn't support this property or method" in general"

Given an object obj, you can test whether property/method prop exists with:

if ("prop" in obj) {
    // do something with obj.prop
}

...noting that the in operator will check inherited properties too. To check only for direct properties use:

if (obj.hasOwnProperty("prop")) {
    // do something with obj.prop
}

"is there a way to check if the variable external exists"

In the case of the external property you mentioned, it will be a property of window if it exists, so:

if ("external" in window) {
   // do something
}

This x in window technique works for global variables including ones provided by the browser and user-defined ones. It doesn't work on local variables.

answered Jul 22, 2013 at 10:35

nnnnnn

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2 Comments

aWebDeveloper Over a year ago

can hasOwnProperty be used for functions too

nnnnnn Over a year ago

Yes. In general terms, a JS object's "methods" are really just properties that happen to refer to functions.

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